May 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 38500] GRB 250516A: Enhanced Swift-XRT position
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40468 SUBJECT: GRB 250516A: Enhanced Swift-XRT position DATE: 25/05/16 17:05:53 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1717 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250516A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 334.60978, -9.11949 which is equivalent to: RA (J2000): 22h 18m 26.35s Dec (J2000): -09d 07' 10.2" with an uncertainty of 2.2 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38499] GRB 250516A: Swift detection of a burst
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40467 SUBJECT: GRB 250516A: Swift detection of a burst DATE: 25/05/16 14:57:08 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), R. Gupta (NASA GSFC), K. L. Page (U Leicester), S. P. R. Shilling (Lancaster U.) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:35:29 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250516A (trigger=1314210). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 334.561, -9.130 which is RA(J2000) = 22h 18m 15s Dec(J2000) = -09d 07' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~5000 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 14:37:13.2 UT, 104.3 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 334.60979, -9.11941 which is equivalent to: RA(J2000) = 22h 18m 26.35s Dec(J2000) = -09d 07' 09.9" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 177 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (5.84 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.8 (+1.47/-1.34) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 108 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.062. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/40467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38498] GRB 250516A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40466 SUBJECT: GRB 250516A: Fermi GBM Final Real-time Localization DATE: 25/05/16 14:46:00 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 14:35:29 UT on 16 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250516A (trigger 769098934.27533 / 250516608). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 333.2, Dec = 0.1 (J2000 degrees, equivalent to J2000 22h 12m, 0d 06'), with a statistical uncertainty of 8.5 degrees. The angle from the Fermi LAT boresight is 27.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38497] GRB 250512B / EP250512a: SVOM/GRM analysis
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40465 SUBJECT: GRB 250512B / EP250512a: SVOM/GRM analysis DATE: 25/05/16 13:34:45 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau, Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by the burst GRB 250512B (SVOM trigger reference: sb sb25051203) at 2025-05-12T11:20:08 UTC (T0), which is also detected by SVOM/ECLAIRs (Pierre Maggi et al., GCN #40439) , Einstein Probe (Zhao et al. GCN 40437) and Konus-Wind (D. Svinkin et al., GCN #40460). With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250512B. The GRM light curve shows that this burst consists of multi-episodes with a T90 of 179 +19/-7 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250512B.png With the localization of ECLAIRs (RA=215.22, DEC=-10.1086), the time-averaged spectrum from T0-3 to T0+50 s (the main episode before the slew) is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.23 +0.42/-0.44 and the cutoff energy, parameterized as Epeak, is 70 +9/-6 keV. The event fluence (10-1000 keV) in this time interval is (3.1 +0.3/-0.2)E-06 erg/cm^2. We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38496] GRB 250515A: GOTO candidate optical counterpart
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40464 SUBJECT: GRB 250515A: GOTO candidate optical counterpart DATE: 25/05/16 09:20:14 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, R. Starling, D. O’Neill, G. Ramsay, A. Kumar, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, and M. Pursiainen report on behalf of GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al 2024) in response to short GRB 250515A (Fermi GBM team, GCN 40462). Targeted observations were performed by GOTO-North (La Palma) beginning at May 15 2025 21:21:20 UT, (+0.58h post trigger) and continuing through to May 16 2025 00:15:21 UT (+3.48h post trigger). 232 images were taken, across 10 unique pointings, covering 471.6 square degrees within the 90% localisation contour. ~60.1% of the total 2D localisation probability was covered, with an average 5-sigma depth of 19.8 mag in the GOTO L-band (400-700nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical source, GOTO25cqo, is identified within the GBM 90% localisation region at RA 10:38:32.5, Dec +19:25:03.1 (J2000). This position is on the 37% probability contour of the Fermi/GBM localisation map. The source was initially detected with magnitude L = 20.17 ± 0.21 mag (+0.71h after the GBM trigger), rising to L = 19.79 ± 0.15 mag at +1.85h post trigger. In a 3rd epoch, taken at t0+2.99 hours, we obtain a 3-sigma upper limit of L > 19.21. We find no strong evidence of this source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). However, we caution that observations to sufficiently constraining depths are not available in the weeks prior to the GRB. We note a marginal flux excess in two ATLAS images taken on 2025-05-01 and 2025-05-03. Visual inspection of these images does not reveal any compelling source, and no significant flux excess was seen in the 7 epochs between these dates and GRB 250515A. From available observations, we cannot confirm whether GOTO25cqo is associated with GRB 250515A, but given its time coincidence and apparent rapid evolution, we encourage further follow-up observations. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/40464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38495] MAXI GRB250515.65: Global MASTER-Net observations report
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40463 SUBJECT: MAXI GRB250515.65: Global MASTER-Net observations report DATE: 25/05/16 02:52:05 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the MAXI GRB250515.65 (trigger No 10849998,21h 14m 24.00s , -80d 30m 00.0s, R=1) errorbox 10 sec after notice time and 40345 sec after trigger time at 2025-05-16 02:41:33 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 50 deg. The sun altitude is -33.6 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the MAXI GRB250515.65 errorbox 79 sec after notice time and 40414 sec after trigger time at 2025-05-16 02:42:42 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 61 deg. The sun altitude is -62.8 deg. The galactic latitude b = -33 deg., longitude l = 312 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2871800 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 40376 | 2025-05-16 02:41:33 | MASTER-SAAO | (21h 16m 32.15s , -80d 50m 43.5s) | C | 60 | 18.1 | 40436 | 2025-05-16 02:41:33 | MASTER-SAAO | (21h 16m 32.15s , -80d 50m 43.5s) | C | 180 | 19.0 | Coadd 40495 | 2025-05-16 02:42:42 | MASTER-OAFA | (20h 13m 48.68s , -81d 25m 05.7s) | C | 160 | 17.6 | 40505 | 2025-05-16 02:42:43 | MASTER-OAFA | (21h 11m 07.77s , -80d 47m 38.7s) | C | 180 | 18.6 | 40454 | 2025-05-16 02:42:52 | MASTER-SAAO | (21h 16m 31.94s , -80d 50m 47.8s) | C | 60 | 18.3 | 40534 | 2025-05-16 02:44:11 | MASTER-SAAO | (21h 16m 31.62s , -80d 50m 49.7s) | C | 60 | 18.2 | 40613 | 2025-05-16 02:45:30 | MASTER-SAAO | (21h 16m 31.26s , -80d 50m 50.6s) | C | 60 | 18.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38494] GRB 250515A: Fermi GBM Final Localization
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40462 SUBJECT: GRB 250515A: Fermi GBM Final Localization DATE: 25/05/15 21:34:47 GMT FROM: R. Hamburg at CNRS/IJCLab <rachel.k.hamburg(a)gmail.com> The Fermi GBM team reports the detection of a likely SHORT GRB "At 20:46:21.91 UT on 15 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250515A (trigger 769034786/250515866). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 154.35, Dec = 23.19 (J2000 degrees, equivalent to J2000 10h 17m, +23d 11'), with a statistical uncertainty of 7.76 degrees. The angle from the Fermi LAT boresight is 69 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40462. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38493] GRB 250424A: COLIBRÍ detection of the associated supernova
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40461 SUBJECT: GRB 250424A: COLIBRÍ detection of the associated supernova DATE: 25/05/15 16:39:06 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), and Margarita Pereyra (UNAM): We have continued imaging the field of GRB 250424A (Cenko et al., GCN Circ. 40224 <https://gcn.nasa.gov/circulars/40224>; Harsha et al. GCN Circ. 40231; Ridnaia et al. GCN Circ. 40243; McKenna et al. GCN Circ. 40249; Zhang et al. GCN Circ. 40252; Nakahira et al. GCN Circ. 40298) at a redshift of z = 0.310 (Saccardi et al. GCN Circ. 40228) to monitor the evolution of the optical transient (Brivio et al. GCN Circ. 40225; Becerra et al. GCN Circ. 40226; de Wet et al. GCN Circ. 40229; Ducoin et al. GCN Circ. 40230; Turpin et al. GCN Circ. 40240; Dutton et al. GCN Circ. 40241; Siegel et al. GCN Circ. 40244; Hu et al. GCN Circ. 40246; Schneider et al. GCN Circ. 40250; Elkabir et al. GCN Circ. 40251; Ghosh et al. GCN Circ. 40263), in search for the possible SN emission, using the DDRAGO wide-field imager on the COLIBRÍ telescope. The field is covered by the Legacy Survey, which reveals an underlying host galaxy with AB magnitudes g=22.60, r=21.98, i=22.05 (Pérez-Fournon et al. GCN Circ. 40227). A GRB-SN at that redshift would be expected to reach peak light between the 8th and the 15th of May (Cano et al. 2017). We hereby report two photometric observations of the optical counterpart obtained in the r- and i-bands. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. An r-band observation consisting of 112x60s exposures was obtained with mean epoch 2025-05-11 06:49:32 UTC (16.998 d after the burst, 12.976 d in the rest frame). We measure r = 21.54 +/- 0.21 mag. An i-band observation consisting of 111x60s exposures was obtained with mean epoch 2025-05-15 06:42:39 UTC (20.993 d after the burst, 16.025 in the rest frame). We measure i = 21.46 +/- 0.12 mag. Both values are clearly in excess of the underlying host galaxy, and indeed an excess emission is obtained when performing image subtraction with respect to the archival Legacy Survey image. Subtracting the host contribution we obtain values of r ~ 22.7 mag and i ~ 22.4 mag which are in agreement to the expectations of a GRB-SN at this redshift with a certain amount of extinction. We consequently suggest that COLIBRÍ is currently detecting the supernova associated with GRB 250424A. Further observations to confirm and monitor the evolution of this GRB-SN are encouraged. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/40461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38492] GRB 250424A: COLIBRÍ detection of the associated supernova
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40461 SUBJECT: GRB 250424A: COLIBRÍ detection of the associated supernova DATE: 25/05/15 16:39:06 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), and Margarita Pereyra (UNAM): We have continued imaging the field of GRB 250424A (Cenko et al., GCN Circ. 40224 <https://gcn.nasa.gov/circulars/40224>; Harsha et al. GCN Circ. 40231; Ridnaia et al. GCN Circ. 40243; McKenna et al. GCN Circ. 40249; Zhang et al. GCN Circ. 40252; Nakahira et al. GCN Circ. 40298) at a redshift of z = 0.310 (Saccardi et al. GCN Circ. 40228) to monitor the evolution of the optical transient (Brivio et al. GCN Circ. 40225; Becerra et al. GCN Circ. 40226; de Wet et al. GCN Circ. 40229; Ducoin et al. GCN Circ. 40230; Turpin et al. GCN Circ. 40240; Dutton et al. GCN Circ. 40241; Siegel et al. GCN Circ. 40244; Hu et al. GCN Circ. 40246; Schneider et al. GCN Circ. 40250; Elkabir et al. GCN Circ. 40251; Ghosh et al. GCN Circ. 40263), in search for the possible SN emission, using the DDRAGO wide-field imager on the COLIBRÍ telescope. The field is covered by the Legacy Survey, which reveals an underlying host galaxy with AB magnitudes g=22.60, r=21.98, i=22.05 (Pérez-Fournon et al. GCN Circ. 40227). A GRB-SN at that redshift would be expected to reach peak light between the 8th and the 15th of May (Cano et al. 2017). We hereby report two photometric observations of the optical counterpart obtained in the r- and i-bands. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. An r-band observation consisting of 112x60s exposures was obtained with mean epoch 2025-05-11 06:49:32 UTC (16.998 d after the burst, 12.976 d in the rest frame). We measure r = 21.54 +/- 0.21 mag. An i-band observation consisting of 111x60s exposures was obtained with mean epoch 2025-05-15 06:42:39 UTC (20.993 d after the burst, 16.025 in the rest frame). We measure i = 21.46 +/- 0.12 mag. Both values are clearly in excess of the underlying host galaxy, and indeed an excess emission is obtained when performing image subtraction with respect to the archival Legacy Survey image. Subtracting the host contribution we obtain values of r ~ 22.7 mag and i ~ 22.4 mag which are in agreement to the expectations of a GRB-SN at this redshift with a certain amount of extinction. We consequently suggest that COLIBRÍ is currently detecting the supernova associated with GRB 250424A. Further observations to confirm and monitor the evolution of this GRB-SN are encouraged. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/40461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38491] Konus-Wind detection of GRB 250512B / EP250512a
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40460 SUBJECT: Konus-Wind detection of GRB 250512B / EP250512a DATE: 25/05/15 11:03:14 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A.Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250512B / EP250512a (EP-WXT detection: Zhao et al., GCN 40437; Yang et al., GCN 40448; SVOM-ECLAIRs detection: Maggi et al., GCN 40439) was detected by Konus-Wind (KW) in the waiting mode at about T0 = T0(EP) = 40803 s UT (11:20:03). A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~8 sigma count-rate increase in the interval from T0+7.4 s to T0+113.3 s. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250512B/ The total burst fluence is 6.68(-2.23,+1.59)x10^-6 erg/cm^2, and the 2.944 s peak energy flux, measured from T0+10.309 s, is 3.08(-1.14,+0.89)x10^-7 erg/cm^2. (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst, measured from T0+7.4 s to T0+113.3 s, can be described by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha > -1.82 and Ep = 114(-37,+57) keV. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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